The purpose of our project is to study the relationships of erythrocytic metabolism with the plastic properties of the membrane with the eventual aim of being able to use this information in the understanding of the pathophysiology of hemolytic disease, the RBC membrane storage lesion, and the biological properties of membranes in general. The specific current studies focus on the mechanism of endocytosis in resealed human erythrocyte ghosts, a phenomenon that requires Mg, ATP, and Ca. It appears that endocytosis is linked to Ca, Mg-ATPase activity and Ca efflux. As a further attempt to understand RBC plasma membrane function we are studying drug induced endocytosis in intact RBC where the drug appears to cause a membrane expansion, invagination, and plasma membrane fusion. This process requires active metabolism and membrane expanding drug, and apparently results in the displacement of Ca from sites present on the cytoplasmic surface of the RBC plasma membrane. The intact RBC appears to control the amount of Ca present at the inner surface of its membrane within very narrow limits to modulate its physical properties. We are therefore studying Ca45 movements within intact RBC. Of importance is the fact that RBC from patients with sickle cell anemia show impaired Ca45 efflux and a five- fold increase in membrane associated Ca. We have also been studying the RBC membrane storage lesion produced by preservation in liquid media and have thus far determined that drug induced endocytosis is a fairly good predictor of in vivo survival of RBC. However, the defect in drug induced endocytosis produced by 6-8 weeks of storage does not include impaired Ca efflux which is surprisingly well preserved in metabolically depleted RBC.